1. Field
The invention relates to tools used for the winning of minerals, particularly mining picks.
2. State of the Art
Tools for the winning of minerals have generally been known for many years. In commercial mining operations, such as longwall coal mining, a plurality of mining picks are typically mounted on a rotatable drum or disk. The picks are mounted such that when the drum or disk is rotated the picks traverse the surface of the strata of earth being mined, thereby digging the surface and releasing the particular mineral being sought. The pick is removable from the rotatable drum or disk so that it can be replaced when it becomes dull, broken or fractured.
The typical commercial mining pick has a shank and a head attached to the shank. The shank is the portion of the pick which is removably attached to the rotatable drum or disk. The head of the pick is that portion which digs the strata of earth being mined when the drum or disk is rotated. Integral with the head, on its leading cutting surface, is a cutting tip. The shank and head are typically manufactured of a hardened metal, such as steel, and the cutting tip is manufactured of a hard and abrasive material. Typical prior art mining picks are disclosed in U.S. Pat. Nos. 4,143,920 and 4,657,308.
It is well known in the prior art to use carbide shaped in either a conical or a wedge design as the hard and abrasive material for the cutting tip. Carbide has the disadvantage of wearing quickly in hard earthen strata, thereby resulting in short tool life and excessive down time in the mining operation for pick replacement. In recent years new materials have been developed which replace the carbide or at least the leading surface of the carbide cutting tip. Through the use of high pressure, high temperature technology, superabrasive materials such as polycrystalline diamond compacts, commonly known as "PDC," and polycrystalline cubic boron nitride compacts, known and sold by General Electric Company under the trademark "BZN.RTM. Compacts," have been produced for use as the leading surfaces in implements for mining, drilling and other cutting operations. PDC materials which are useful for these purposes are disclosed in U.S. Pat. No. Re 32,380 which teaches a PDC material which is sold by General Electric Company under the trademark STRATAPAX.RTM., U.S. Pat. No. 4,224,380 which teaches a thermally stable PDC, and U.S. Pat. No. 4,738,689 which teaches a coated thermally stable PDC, the latter materials being sold by General Electric Company under the trademark GEOSET.RTM.. BZN.RTM. Compacts are disclosed in U.S. Pat. Nos. 3,767,371 and 3,743,489. The foregoing General Electric Company patents are assigned to the same assignee as the present invention, and are incorporated herein by this reference.
The superabrasive material is usually backed by and bonded to a metallic substrate which is manufactured of a harder material than the head of the pick. The metallic substrate is also bonded to the head of the pick so that the metallic substrate acts as a layer between the superabrasive material and head. The metallic substrate backing is typically oriented to provide mechanical support for the superabrasive material to reduce fracturing thereof and to reduce stress on the superabrasive material metallic substrate bond. Metallic substrate materials which have been used in the past are carbide or a hard cemented metal such as cemented carbide.
The shape of the prior art PDC or BZN.RTM. Compact is typically one having flat surfaces, such as a disk or cylinder. If the compact is shaped in the form of a disk, it is bonded to the substrate along one of its flat surfaces, with the opposite nonbonded flat surface being the lead surface which comes into contact with strata of earth in the mining or drilling process. If the shape of the compact is a cylinder, the cylinder is typically imbedded along its longitudinal axis in the substrate, leaving an end surface of the cylinder exposed out of the substrate which acts as the digging surface. The use of a cylindrical PDC imbedded in a cemented metal substrate is taught by South African Patent Application Serial No. 846960. The size of the PDC or BZN.RTM. Compact used in these prior art PDC and BZN.RTM. Compact pick designs and the fabrication techniques which are required result in approximately a tenfold cost increase of prior art PDC or BZN.RTM. Compact mining picks over the prior art non-compact mining picks, while the present invention results in approximately only a fourfold cost increase.
Prior art picks using a broad surface for the digging surface dig through a crushing or pawing action. In carbide tiped picks the broad digging surface results from the wear of the carbide. In PDC or BZN.RTM. Compact tipped picks, a broad flat surface of the compact is the digging surface. The crushing or pawing digging action results in the undesirable effects of high air concentrations of particulate dust, high heat generation, high energy consumption and relatively short tool life.